In single core submarine cables, there is used an armouring, normally formed by copper wires (though steel wires may also be used), to provide mechanical strength to the cable since the latter will be subjected to considerable tension when placed in its operative position at sea. Accordingly, the armouring plays a vital role for the strength of the cable. The armouring also acts as a carrier of electric current, and the current conducted by the armouring may be very large, even as large as the one conducted by the conductor of the cable. Apart from the armouring, sea cables also typically comprise a water barrier made of a layer of a material provided for the purpose of preventing water from reaching and having a detrimental effect on the electric insulation that is provided around the conductor. The water barrier is positioned underneath the armouring, normally divided from the latter by a polymer layer, and made of metal, such as aluminium or lead.
Cable joints are used for the purpose of interconnecting cables. Since some parts of the cable, such as the water barrier and the armouring, are stripped off from the cable in the region of the joint, the joint enclosure must provide for the functionality of said parts. Accordingly, joint enclosures are provided with elements that functionally correspond to the armouring and the water barrier. Prior art comprises joints in which there is provided a first casing that has as its task to provide the function of the water barrier and also to withstand the hydrostatic pressure that can be expected at the level at which the cable is to be located when in its operative position. Another, second casing is provided around the first casing and has the task of mainly adopting the mechanical load that the cable armouring is subjected to. The second casing may be a set of wires or may have more of a tubular design. Typically, the armouring of the cables is cut off at a certain point and the remaining armouring wire ends are positioned on a cone-shaped ring that forms a part of the joint enclosure. A further ring element is slid onto the cone-shaped ring such that the armouring wires are clamped between the inner periphery of the further ring element and the outer periphery of the cone-shaped ring. Screws extending in a generally radial direction are used for tightening the further ring element against the cone-shaped ring.
The enclosure is subdivided in two parts, each of which is applied to a respective cable. During assembly of the enclosure, after joining of the cable conductors in a manner known per se, the two enclosure halves are joined. Accordingly, in the case of an inner first casing and an outer second casing, each casing is subdivided in two halves, whereby the first casing is assembled first and the second casing is assembled subsequently and outside the first casing.
Since, normally, the second casing is made of a material that is less conductive but mechanically stronger material than the material of the armouring, it is not able of conducting the same current as the latter. Therefore, a further conducting element, typically a copper wire arrangement or the like, is connected to the ring to which the armouring wires are connected and led, outside the second casing, from one end of the joint enclosure to the other end, where it is correspondingly connected to the other end of the joint enclosure. Outside the second casing, and around said further conducting element, there is provided a filler medium such as asphalt or the like, which in its turn is enclosed in a cone-shaped body (typically two conical protective bodies), typically made of metal, that cover the ends of the joint enclosure and prevents bending of the cables in those regions. Around the enclosure and the protection cones, a heat shrink of an electrically insulting material may be arranged for the purpose of preventing galvanic corrosion in the joint, especially corrosion caused by the use of steel in the second casing and the copper of the armouring, and also for protecting the joint enclosure against damage and wear.
The whole joint, including the joint enclosure, is rather large, having a length of several meters, and there is a desire to make it as compact as possible without thereby sacrificing its functionality. It is also a desire to facilitate the assembly of the joint arrangement as far as possible.